1. Field of the Invention
The present invention relates to railway air system air dryers and, more particularly, to an air dryer control system having a sleep mode to prevent the depletion of air and power during idling times.
2. Description of the Related Art
A typical “twin-tower” desiccant-type air dryer includes two drying circuits that are controlled by valves. Wet inlet air flows through one circuit to remove water vapor, while dry product air counter flows through the other circuit to remove the accumulated water and regenerate the desiccant. Inlet and outlet valves for each pneumatic circuit are responsive to controlling electronics to switch the air flow between the two circuits so that one circuit is always drying while the other is regenerating. The air dryer may include a pre-filtration stage with a water separator and/or coalescer positioned upstream of the drying circuits. The pre-filtration stage removes liquid phase and aerosol water and oil that can accumulate in air supply system as a result of the compression of ambient air by the locomotive air compressors. A pre-filtration stage includes a drain valve that is used to periodically purge any accumulated liquid. For example, a typical pre-filtration drain valve actuation cycle might command a purge (open) for two seconds every two minutes.
When a locomotive is parked, the driver will usually open the main circuit breaker and shut down the auxiliary electrically powered equipment, which includes the air dryer. Under certain circumstances, however, the locomotive may be parked or idled for an extended period with the electrical power left on. If the diesel engine or air compressor is turned off, the pre-filtration drain valve and desiccant regeneration valves will continue to cycle and will eventually deplete the main air reservoir and/or the locomotive battery. Some air supply systems address the problem of electrical power depletion by only operating the air dryer valves when the air compressor is running. This solution, however, does not fully address the problem, as it can result in inefficient drying of the air when it is operating. For example, air can still flow through an air dryer when the compressor is off. In addition, there are many instances when the compressor is turned on but no air is actually flowing through the air dryer such that operation of the valves is wasteful. Finally, in a multiple locomotive consist where all of the locomotives are coupled together by a main reservoir trainline, the other locomotives in the consist can be supplying compressed air to the locomotive whose compressor is off. Accordingly, there is a need in the art for an air dryer control system prevents the air dryer from unnecessarily venting compressed air or wasting electricity when the locomotive air supply system is intended to be idle.